I wouldn't worry for your vacations. Here are two recurrent periods of strikes:

- Generally, strikes start in unis and high schools in the far end of September, and, depending on the year, they may develop into fully-grown national riots in public companies (SNCF) then private companies, or if there's no political following, they die off with the October school holidays. This year I'm forecasting a lot of following, because Macron intends to take controversial decisions about employment laws during this summer.

- Flight strikes are rather planned for Christmas holidays (20 Dec-3 Jan). They have internal reasons and are generally not related to the October strike season. So, your September holidays are safe ;)

There's been a call for strikes to protest against the labor code reforms by several syndicates and far left parties (PC, Mélenchon's Insoumis). Expect the usual circus, but I don't think it'll be too bad. There were already some labor reforms under Hollande, and they went through. Now there's an even bigger majority for it. But syndicates and the far left have to go through the motions and protest on this. Get some popcorn, enjoy the show (not too close), you may see a traditional French protest while here. IIRC it should be around mid-September.